Patellofemoral joint stress during running in females with and without patellofemoral pain. Knee. (2012)

Abstract
Patellofemoral pain (PFP) is a common complaint among female runners. The etiology for PFP is frequently associated with increased patellofemoral joint stress (PFJS) and altered hip and knee joint kinematics during running. However, whether PFJS during running is increased among runners with PFP is unknown. The primary aim of this study was to compare PFJS during running among females with and without PFP. We also compared hip and knee transverse plane kinematics during running due to their potential influence on patellofemoral contact area and PFJS. Three dimensional hip and knee running kinematics and kinetics were obtained from 20 females with PFP and 20 females with no pain. Patellofemoral joint stress during running was estimated using patellofemoral contact area and a sagittal plane patellofemoral joint model previously described. Patellofemoral joint stress, PFJS-time integral, and hip and knee transverse plane kinematics at the time of impact peak and peak ground reaction force were compared between groups using a multivariate analysis of variance. The results show that peak PFJS and PFJS-time integral were similar between groups. Peak knee flexion angle and net knee extension moment were not different between groups. However, females with PFP demonstrated hip internal rotation that was 6° greater (P=0.04) when ground reaction forces were greatest. The extent these results are influenced by compensations for pain is unclear. However, if increased PFJS contributes to the etiology or exacerbation of PFP, interventions to minimize altered transverse plane hip kinematics may be indicated among runners who demonstrate this characteristic.

My comments:

This study looked to see if there was increased patellofemoral compressive stresses during running on women with and without patellofemoral pain.  They did not find any significant differences.  However in their comments they noted that the mathematical model they used did not account for internal and external rotation stresses at the hip and knee (which were found to be significant) and thus their model might have underestimated real life patellofemoral stress.  Most significant findings were hip internal rotation that was 6 degrees greater than normal, and a subsequent knee external rotation of 4.8 degrees.

The findings are inline with earlier research that notes hip external rotation and hip abduction strength is particularly weak in runners suffering patellofemoral pain and as such physical therapy programs programs should make use of progressive resistance exercise to the hips, legs, and core to complement ones running program.  Passive modalities and/or various massage techniques are likely to have little effect outside of psychological comforting and placebo.  EMS, however is a useful to both decrease pain and further increase strength to targeted muscles.